Measuring apparatus



Oct. 5, 1943. J. D. RYDER 2,331,138

MEASURING APPARATUS Filed Jan. 25, 1942 5 sheets-sheet 1 Suuentor JOHN D. RYDER Oct. 5, 1943.

J. D. RYDER MEASURING APPARATUS 5 Sheets-Sheet 2 Filed Jan. 23, 1942 Fl Q 2 Snuentor JOHN D. RYDER Oct. 5, 1943. J. D. RYDER 2,331,138

MEASURING APPARATUS Filed Jan. 23, 1942 5 Sheets-Sheet 3 nuemor F|G 4 JOHN D. RYDER Bg (WM/MM@ Oct. 5, 1943.

J. D. RYDER 2,331,138 MEASURING APPARATUS I Filed Jan. 23 1942 5 Sheets-Sheet 4 G I D T |39 (4 l |o| s 1 a lll. ||O 108 |09 Q9 lo? salsas "JGBA- "L Y 2 l ne TM5 ||9 122A Snuenfor B JOHN D. RYDER I H FIG. 5

Oct. 5, 1943. J. D. RYDER l 2,331,138

MEASURING APPARATUS Filed Jan. 23. i942 5 sheets-sheet 5 lOl IOOA

n Y 142A v JOHN D. RYDER dttorneu Patented Oct. 5, 1943 MEAsUamG APrARA'rUs John D. Ryder, Ames, Iowa, assignor to Bailey Meter Company, a corporation of Delaware Original application September 13, 1939, Serial No. 294,570. Divided and this application AJanuary 23, 1942, Serial No. 427,846

8 Claims. (Cl. 1'71-95) This invention relates to measuring apparatus and forms a continuation-impart of my application Serial No. 77,488 filed May 2, 1936, now Patent 2,215,254, as well as being a division of my copending application Serial No. 294,570, filed September 13, 1939, as a continuation-in-part of my application Serial No. 77,488. More particularly this invention relates to electrical measuring apparatus of the potentiometric type wherein a potential generated ln correspondence with the magnitude of a condition is balanced against a known variable voltage produced by a potentiometer so that the latter becomes a measure of the former. 'Apparatus of this general type is particularly adapted to the measurement of temperature, a thermocouple being used to produce a potential varying as the temperature to be measured.

In the conventional potentiometer pyrometer the portion of the slide wire resistance of the potentiometer in circuit with the thermocouple is automatically varied so that the potential generated vby the thermocouple is opposed by an equal and opposite potential. An unbalance between the thermocouple and slide wire potential is detected by means of a galvanometer connected in circuit with the thermocouple. A defiecting member of the galvanometer is used to control a suitable reversing means, such as an electric motor Awhich positions a contact along the slide Wire and varies the portion of the slide wire in circuit with the thermocouple to restore the said potentials to equality and return the deflecting mem-ber of the galvanometer to predetermined null or zero position. The portion of the slide wire in circuit with the thermocouple is then a measurejof the thermocouple potential,

and inferentially of the temperature to which the themocouple is responsive.

As a galvanometer is extremely delicate, it isv highly preferable that such contacts as may be associated therewith to control the reversing slide wire motor do not carry the entire current necessary to effect operation of the motor; but

. that suitable amplifying means bev incorporated so that a relatively minute current under the direct control of the galvanometer may be amplified to sufficient magnitude to effect proper operation of the motor.

In my prior Patent 2,015,968 I have illustrated and described a novel potentiometer pyrometer wherein the slide wire contact is positioned by a reversing motor having opposed wound fields. Energization of one -iield effects operation of the motor in one direction, whereas energization of the opposed field effects operation in the opposite direction. 'I'he energization of each field is controlled by means of a suitable electron discharge device, the output circuit of which is in-v ductively coupled therewith and the input circuit of which is controlled by the galvanometer. By means of the electron discharge devices andthe inductive couplings it is possible to amplify the current directly controlled by the galvanometer many times, and thus produce accurate positioning of the reversing motor without undue burden on the galvanometer or contacts associated therewith.

My present invention relates to a modification of that disclosed in my said prior patent. In accordance with the instant invention I employ a reversing induction motor having a continuously energized A. C. field Winding and opposed shading pole windings. As known, short circuiting of one pole winding of such a motor produces rotation of the motor in one direction, and short circuiting of the opposed pole winding produces rotation in opposite direction. I have found that I may effectively short circuit the pole windings of such a motor by connecting in the circuit of each Winding the primary of a. step-up transformer, and selectively short circuiting the secondaries of the transformers in accordance with the direction of rotation desired. The short circuiting of eith-er secondary Will sufficiently reduce the impedance of the primary that the pole vWinding'connected in'circuit therewith Will be eil'ectively short circuited. In one type of opposed shading pole motor I have employed, 22 Volts exist across the pole windings when open circuited. This voltage is stepped up by means of a transformer so that there is approximately 375 volts across Vthe secondary. Upon short circuiting the secondary of the transformer the impedance of the primary is decreased so that approximately 5 volts exist across the pole winding.

Further, in accordance with the present invention the secondaries of the transformers are connectedin the output circuits of suitable electron discharge devices, the i-nput or `grid circuits of which are controlled by the galvanometer. Under normal conditions, that is when the galvanometer needle is in neutral position, the grids of the electron discharge devices may be maintained sufficiently negative so that the devices are non-conducting- Deiiection of the galvanometer needle in one direction however causes the grid of a selected one of said devices to become less negative, thereby rendering the connected electron discharge device conducting, and

causing the energization of the associated pole winding of the induction motor. Opposite defiection of the galvanometer needle causes energization of the opposed pole winding through similar means.

Such in .general is the nature of the apparatus whichI herein disclose. ,For a more complete understanding of my invention, and for an appreciation of the details of operation and construction, reference should be made to the descriptionto follow and to the drawings in which: Fig. l1 illustrates schematically a basic circuit arrangement embodying my'invention.

Fig. 2 diagrammatically illustrates a circuit arrangement substantially the same as that illus-v trated in Fig. 1 together with some constructional features.

Fig. 3 is a detailed view of an induction motor having opposed shading pole windings and associated apparatus diagrammatically illustrated in Fig. 2.

Fig. 4 illustrates a somewhat modied form of circuit `arrangement over that disclosed in Figs. 1 and 2.

Fig. 5 illustrates a further embodimentof my invention diering in mechanical details; but

Aemploying the same circuit arrangement as shown in Figs. l and 2.

Fig. 6 illustrates a. further embodiment of my invention employing the mechanical construction illustrated in Fig. 5 and the circuit arrangement shown in Fig. 4.

Referring to Fig. 1, I therein illustrateV my invention arranged to position an indicator ||3 relative 'to a scale ||4 to exhibit the temperature to which a thermocouple T is sensitive. The thermocoupleA T is connected to a conventional potentiometer circuit comprising a source of potential ||5 and a slide wire. resistance H6 at junction ||8 and contact IIS. The contact H9 is positioned along the slide wire resistance H6 and the indicator |3 vis moved relative to the scale I4 by a nut |20 threaded to a screw |2| rotated by an induction motor |22 having op- 'posed wound shading poles |23, |24 and a condevice |25 rendered conducting, by virtue of the current induced in the secondary, the impedance of the primary of the transformer |25 is reduced suiciently so that the winding |23 becomes substantially short circuited and the motor |22 rotates to move the nut |23 in desired direction. Conversely, when the electron discharge device |3| is short circuited, the winding |22 is substantially short circuited, moving the nut in opposite direction. I have found, for example, that approximately 25 volts exist across the windings |23, |24 when open circuited. By employing an approximately 15 to 1 transformer I am able, upon rendering the electron discharge devices |26, |3| conducting, to sufiiciently reduce the impedance of the primaries of the transformers so that approximately 5 volts exist across the windings |23, |23,

The grids |28, |33 are shownconnected to the common conductor |35 through a source of potential |36 and resistances |31, |38 respectively. The source of potential |35 may be considered as a conventional showing of any grid bias arrangement so that normally the grids |28, |33 are negative with respect to their cathodes |29, |34 and the electron discharge devices |26, |3| non-conducting.

Connected in circuit with the thermocouple T is a galvanometer G having a movable member |39.

which upon displacement from the neutral position in one direction engages acontact |43, and upon displacement in the opposite direction engages a contact |4|. A conductor |42 connects the movable member |39 with the'conductor. |35 between the source of potential |39 and the cathodes |29, |34. When the movable member |39 engages the contact |4| the source of potential |36 and resistance |30 is shunted out, the grid |33 bein-g rendered less negative and a. potential equal to that of the cathode |34 impressed thereon. With the grid |33 at the same'potential as the cathode |34 the device |3| is rendered conducting during the half cycle of the alternating current in the output circuit when the plate |32 .is positive with respect to the cathode |34. During the half cycle, when the cathode 34 is positive with respect to the plate |32, the device |3| is non-conducting regardless of the potential of the grid |33.

While the device |3| is conducting the secondary winding of the transformer |30 is short circuited, thereby reducing the impedance of the primary winding sufficiently so that the winding |24 of the the primary of a transformer |25, the secondary electron discharge device |26 having an anode |21. a. grid |28 and a cathode |29. The winding |24 is similarly connected in circuit with the primary of a. transformer |30, `the secondary Vof which is connected in the output circuit of an electron discharge device |3| having an anode |32, a grid |33 and a cathode |34. The cathodes |29 and |34 are connected to a common conductor |35 and may, .if desired, be provided wltha heating element to maintain them at a desired working temperature as well known.

When the electron discharge devices |26 and |3| are non-conducting, the impedance of the primaries of the transformers |25, |30 is sumc'ent that the windings |23, |24 are substantially open circuited, and the motor |22 is not motor |22 is effectively short circuited, effecting rotation of motor |22 in desired sense. Displacement of the movable member |39 in opposite direction from the nullor zero position so that it engages contact |40 serves to shunt out the source |36 and resistance |31, so that the grid |28 is rendered less negative causing effective short circuiting of the winding |23, and causing the motor |22 to operate in opposite direction.

In operation, assuming that the potential drop between the junction I8 and contact I9 through the slide wire resistance ||6 is equal to, but opposed to that generated by the thermocouple T, the movable member |39 of the galvanometer-G will be in the mid or neutral position. Upon a change in temperature of the thermocouple T, for example an increase, the movable member |39 of the galvanometer G will be displaced from the neutral position and engage contact |4|. The electron discharge device |3| will be rendered conducting, winding |24 eectively short circuited and motor |22 will rotate in a direction to move ing.

Conversely, assuming a decrease in temperature of the thermocouple T, the movable member |39 will be displaced from the neutral position to engage contact |40 rendering the electron discharge device |26 conducting, which will serve to substantially short circuit the winding |23 so that the motor |22 will rotate in a direction to decrease the potential drop between the junction ||3 and contact ||9 until the movable member |39 is again restored to the neutral position.

As taught in my parent application Serial No. 77,488, thesource |36 may comprise a source of alternating current potential suitably phasedwith respect to the alternating current in the output circuits of the devices |26 and '|3I, s o that normally the grids |28, |33 are negative during the half cycle when the anodes |21, |32 are positive with respect to the cathodes |29, |34, thereby maintaining the devices |26, |3| non-conducting. With such an arrangement during the remaining half cycle the grids |28, |33 will be positive with respect to the cathodes |29, |34. However, the devices will remain non-conducting as during this half cycle the plates |21, v|32 will be negative with i. respect to the cathodes |29, |34. It will be evident therefore that during this half cycle it is immaterialwhat relative voltage the grids |20, |33 assume with respect to the cathodes |29, |34.

Further, as well known, improved operation of a potentiometric system may be obtained by eecting periodic operation of the reversing means moving the contact relative to the slide wire; and further by relatively moving the contact and slide wire` periodically by amounts corresponding to the deflection of the galvanometer needle from the mid or neutral position. In my prior Patent 2,015,968 I disclose apparatus whereby the input .circuits of suitable electron discharge devices,

such as illustrated at |26, |3| may be so controlled in correspondence with the deflections of a galvanorneter needle that the output circuits thereof will be periodically rendered conducting for time increments corresponding to the deflection of the galvanometer needle from the mid or neutral position.

In Fig. 2 I have illustrated the circuit'arrangement disclosed in Fig. l but incorporating an alternatingr current grid bias. Further in Fig. 2 I have illustrated the mechanism disclosed in my prior Patent 2,015,968 whereby I secure periodic energization of the input circuits of the electron discharge devices |26, |3| time quantitatively in correspondence with the amount of deflection of the galvanometer needle |39 from the mid or neutral position. By virtue of the fact that short circuiting of the winding |23 or |24 results in operation of the motor |22 at substantially constant speed it follows that if the input circuits are energized time quantitatively in correspondence with the amount of deflection of the galvanometer needle |39 from the neutral position, the desideraturn will be secured of having the slide wire contact ||9 periodically adjusted in amount corresponding to the amount of deflection of the galvanometer needle;

Referring to Fig. 2 I will first describe the circuit arrangement, whereby-thel grids |28, |33

' the electron discharge device 3| non-conductare provided with alternating current so phased that normally, during the half cycle when the plates |21, |32 are positive the grids are negative; and during the half cycle that the plates are negative the grids are positive with respect to the cathodes |29, |34. The potential normally effective on grids |29, |33 is obtained from an a1- ternatin'g current source |2 through a transformer l60 and the reslstances |31, |38. 'I'hecathodes |29, |34 are connected to a terminal 66A and the grids |23, |33 to an opposite terminal 69B of the secondary of the transformer 68. Normally therefore during one half cycle the grids |23, |33 will be positive with respect to the cathodes 29, |34

and during the remaining half cycle negative with respect thereto.

During the half cycle that the grids |20, |33 are positive with respect to the cathodes |29, |34 I cause the plates |21, |32 to be negative with respect to. the cathodes |29, |34 by properly phasing the A. C. eldQwinding |22A of the motor |22 and transformers |25 and |30. Thus notwithstanding that the grids |28, |33 are positive the electron discharge devices |26, |3| will be non-conducting. As shown, terminals |25A, |'30A of the secondaries of transformers |25, |30 are maintained at the potential of cathodes |29, |34. The phase of the field winding |22A and of the secondaries of the transformers |25, |30 is so arranged that during the half cycle when the grids are positive relative to the cathodes the terminals |25B, |3013 of the secondaries of transformersl |26, |3| connected to the plates |21, |32 are negative and no current will pass through the electron discharge devices |26, |3|.

In order to render one or the other of the devices |26, |3| conducting, selectively in correspondence with the deflections of the galvanoxn-Y eter needle |39 from the mid or neutral position, I render the grids less negative yduring the half cycle when the plates are positive with respect to the cathodes. As shown, the galvanometer needle |39 is connected to the cathodes 29, |34 through the conductor |42 in which is a suitable resistance 62. Upon the deflection of the galvanometer to the right, as shown in Fig, 2, the contact |40 is engaged and the resistance |31 bypassed, thus impressing upon the grid |28 a po- 'tential substantially equal to that of the `cathode |29. The device |26 will thus be rendered conducting and effect operation of the motor |22 in predetermined direction as heretofore described. Deflection of the galvanometer needle and away from each other by the agency of similar but oppositely positioned cams 54, 55 rigidly attached to a shaft 56 rotated at constant speed by the continuously operated motor 3|. The scissors bars 5|, 52 are provided at their lowermost ends with rollers, the one riding the surface `of the cam 54 and the other the surface of the cam 55. The scissors bars further carry respectively the contacts |4|, I 39 insulated therefrom and from each other.

' The galvanometer G as schematically illustrated in Fig. l is shown in Fig. 2 as being of the suspended type and properly located relative to a permanentmagnet 57. Normally the needle 59 of the galvanometerisfree to deect in accordance with the diierence of potentials generated by the source to which the'galvanorneter is connected, and that portion of the potentiometer circuit spanned. Periodically, however, the needie i139 is clamped between a stationary portion 55 and a movable bar 59 which is pivoted at a point 65. 'I'he pivoted portion carrying the movable bar 55 is reciprocated or angnlarly moved relative to the pivot Bil by means of a constantly revolving cam Si secured to the shaft 55. Thus periodically upon each revolution of the cam 5l the needle i3@ will be clamped lightly between the stationary member 55 and the movable reciprocating bar 59 and for a portion of each revolution of the cam 5i.

Immediately after the needle S39 has been so clamped, the position of the cams 5d, 55 relative to the cam 5i is such that the scissors arms 5i 52 move toward each other. When, as shown, the galvanometer needle |59 is in the mid-position, indicating a balance between the two poten tlals, the scissors arms 5i, 52 will follow the complete periphery of the cams 55, 55 and neither the contacts d5, 5B will engage the needle E39. However, if the needle is deilected through action of the galvanometer G either to the right or to the left, then the adjacent scissors arms will follow the periphery of the associated cam until the contact carried by the scissors arm reaches the needle. Further motion of the scissors arm toward the other will then be prevented by the galvanometer needle, and the engaged contact will remain in engagement with the needle until the scissors arm is again picked up by the associated cam and moved away. At a predetermined definite point in the outward travel of the scissors arms the galvanometer needle E35 will be released from clamping engagement and be free `to deect either further away or return toward the predetermined neutral position, and until it is again clamped as a scissors arms travel toward each other on the next cam' cycle of revolution.

it is evident that by proper shaping of the cams 555, 55 'the length of time the scissors arms are in contact with the galvanometer needle i5@ may be made directly proportional to the amount oi deviation of the needle from the mid position, which in turn is proportional to the difference of the opposed potentials. If desired, one of the cams, for example, 513, may be made of a liierent shape than the other cam, for example 55, whereby the length of contact for a given deection of the galvanometer needle in one direction may be made different from that for the same amount of deflection of the galvanometer needle in the opposite direction. It is further evident that the cams 55, 55 may be made of any'desired shape so that the length of engagement between the contacts carried by the scissors arms and the galvanometer needle may bear any desired functional relation to the amount of deviation from the neutral or lmid-position of the galvanoineter needle.

1n each cycle of operation the galvanometer needle B35 will engage either the contact lli@ or i5! in accordance with the direction of the deection of the needle from the mid or neutral position, and such engagement will be time quantitativelv in accordance with the amount of deassises ection of the needle from the neutral position.

Such engagement will render a selected one of lthe devices 26, i3l condcting and thus short circuit the opposed pole winding 'E23 or i125 to effect rotation of the motor B22. Such rotation will be in proper direction to rebalance the'potentiorneter, thatis to move'the contact i i9 along the slide wire i lt so that the potential determined by that portion of the slide wire spanned is mainl tained equal to that generated by the thermocouple T.'

n Figs. 1 and 2 have shown the motor 522 and associated apparatus diagrammatically. In Fig. 1 the motor is shown as positioning the index iis along a scale lill. In Fig. 2 1 have illustrated the motor i122 as 'positioning ran index H3A adapted to indicate the temperature in cooperation with a lsuitably graduated-scale ilLA and to record the-'same in cooperation with a suitably graduated chart lili which may be rotated at desired speed by'any suitable clock'means (not shown). y

In Fig. 3 I haveshown in perspective a-detailed view in more commercial form of the motor l22 and associated apparatus. The motor iai-is mounted on a base 263i secured to thel rear of a panel 2li?. `Securedv to the shaft 2li@ driven 4by the motor i122 is a ilat disc 283A carrying in' its outer periphery the slide wire H5. The contact H9 is carried in a resilient arm 2M secured to a stationary adjustable bracket 205. Rotation of the motor H22 positions the contact il@ relative to the slide wire il@ and varies the amount of the latter spanned by the thermocouple connections.

The rotor of the motor D22 rotates at relatively high speed in the order of 2000 or more revolutions per minute. As shown, the slide Wire lili is however positioned less than a complete revolution. The shaft 263 is therefore not driven directly from the rotor ofthe motor l22 but through an integral gear reduction unit i22B, so

that the angular speed of the shaft 203 is in 1 the order oi a few RPM.

The index ll5A is angularly positioned by the motor l22 through a cam 255 secured to the shaft Zeil. cam follower 21TH and shaft 258 journaled Ain the panel 252 and a bearing Zii. As known,

a non-linear relation exists between the temperature to which a thermocouple is subjected and the emf produced thereby. The cam 2% may be given a non-linear shape corresponding to the relation existing between temperature and thermocouple emi so that the index H3A will be 'positioned in linear relation to the temperature rather than in linear relation to the emf generated by the thermocouple. As evident to those skilled in the art the panel 202 may be provided with suitable chart holding means on which the chart 82A as shown in Fig. 2 may be mounted. Likewise suitable means f or rotating the chart l may be provided. l

In Figs. l. and'2 I have illstrated my invention wherein the electron discharge devices E25, i3! are normally non-conducting and consequently the pole windings 23, E24 are .open circuted. 1n Fig. 4 I illustrate a modified circuit arrangement wherein the devices H26, i3! are normally conducting 'and the pole windings H23, H24 normally short circuited. Such concurrent energization of the pole windings 23, i243 does not produce rotation of the motor E22 however, as both windings are equally energized and act in opposition to each other. Upon engagement of the galvanometer needle l 39 with the contact 14D, for example, the device l 26 is rendered non-conduct- Vresistances |31 and |38 respectively. When'the galvanometer needle |39 does not. engage .either the contact |40 or |4|, during each half cycle when the anodes |21, |32 are positive with respect to the cathodes |29, |34 the electron discharge A devices |20, |3| will be conducting. As heretofore described such intermittent operation of the electron discharge devices will effectively short circuit the windings |23, |24 of the motor |22.

In this embodiment, it willbe noted, the galvanometer needle |39 is connected by a conductor |42A through the resistance 62 to the terminal 88B of the secondary of the transformer 68, which is opposite in'phase to the terminal 68A to which cathodes |29, |34 are connected. Upon engagement of the galvanometer needle |39 with the contact |40, for example, during the half cycle when the anode |21 is positive with respect to the cathode |29 the grid |28 will be rendered sulliciently negative with' respect to the cathode |29 as to render the electron discharge device |26 non-conducting. Throughout the duration of such engagement betweenv the galvanometer needle |39 and contact |40 the pole winding |23-wil1 be deenergized and the motor |22 rotate in predetermined direction under the action of the pole winding |24. Engagement of the galvanometer needle 39 with the contact |4| renders'the electron discharge device |3| non-conducting throughout the duration of such engagement, thereby permitting the motor |22 to rotate in opposite direction under the action of the pole winding |23.

I have illustrated in Fig. 4 the same galva-` nometer contacting mechanism as illustrated in Fig. 2, so that the motorv |22 will be periodically positioned, time quantitatively in correspondence with the amount of deflection of the galvanometer needle |39 yfrom the neutral position.

In Fig. 5 I show a further modied form of my invention somewhat different as to vmechani cal arrangement of .the galvanometer contacting mechanism than the embodiments heretofore described but embodying the same basic principles. Referring to the drawings, the galvanometer needleA |39 is arranged to be positioned along a stationary horizontal anvil |00A in correspondence Withdilerences in the potential generated by the thermocouple T and that in the portion of the slide wire resistance ||6 determined by Athe position of the contact ||9. Two feelers |0| and |02 are adapted to be reciprocated between definite limits vabout a bearing |05 by a cam |03 continuously rotated at constant speed by a motor |04. During each reciprocation one or the other, or both of the feelers |0|, |02 engage the galvanometer needle |39 and depress it against the anvil |00A when further movement of the feelers is arrested. As shown, the feelers are provided with oppositely disposed sloping contact they move downwardly under the influence of gravity, and are simultaneously disengaged from the galvanometer needle as they are positioned upwardly by the cam |03. If the galvanometer needle is deflected to the left, as viewed in the drawings,` the downward course of the feeler |0| will bearrested and it will remain in engagement with the galvanometer needle for a time duration corresponding to the deflection of the galvanometer needle from the mid or neutral position. Conversely, if the galvanometer needle is deflected to the right, as viewed in the drawings, the downward course of the feeler |02 will be arrested and it will remain in engagement with the galvanometer needle for a time duration corresponding to the deflection of the galvanometer needle from the mid or neutral position.

The feelers |0|, |02 are reciprocated by the cam |03 through a follower |01 pivoted about the bearing |05. The follower carries a projection 0 made of insulating material in which are threaded adjustable contacts |08 and |09. The contact |08 normally engages a contact carried in an insulated forwardly extending projection on the feeler |0|. The contact |09 is normally in engagement with a similar contact ||2 `carried by the feeler 02. While the feeler I0| is in engagement with the galvanometer needle |39 contacts |08| are disengaged, and while the feeler |02 is in engagement with the galvanometer needle, conta'cts |09-I I2 are disengaged. It is apparent therefore that the arrangement provides for the periodic engagement of contacts |08|| for a time increment corresponding to the deflection of the galvanometer needle |39 to the left of the mid or neutral position, and for periodic disengagement of contacts |09| |2 for a time increment corresponding to the deflection of the galvanometer needle to the right of the mid or neutral position.

By adjustment of the contacts |08, |09 engagement with contacts ||2 may be maintained throughout the cyclic course of the follower |01 when the galvanometer needle |39 is in the'neutral position. However, I usually find it preferable to have both contacts |08| and |09-I |2 disengage for 'a small increment of time when the galvanometer needle |39 is in the neutral position. In this manner I may provide for a more sensitive control of the motor |22, for upon the slightest deflection of the galvanometer needle from the neutral position a difference in time duration of disengagement of contacts |08||| and |09||2 will be effected. If the contacts |08||| and |09,-||2 were permitted to remain in engagement throughout the cyclic course of the follower |01 when the galvanometer needle is in the neutral position unless a high degree of care was exercised in adjustment; of the apparatus it would be possible for the galvanometer needle |39 to deflect slightly to the right or to the left from the neutral position and still have the contacts |08| and ||0| I2 remain in engagement.

In the modification of my' invention shown in Fig. 5 the contacts |||||2 are connected by conductor |42A through resistance 62 to the terminal 68A. The electron discharge devices |26, |3| are therefore maintained normally conducting. When contact |09 disengages contact ||2 the electron discharge device |26 is rendered nonconducting, as the grid |28 is then connected through resistance |31 to the terminal 88B of the secondary of transformer 68. Similarly when contact |08 disengages contact the electronv discharge device i3! is rendered non-conducting. As described with reference to the circuit arrangement disclosed in Fig. 4 when either the electron discharge device |26 or |3| is rendered non-conducting the motor |22 will rotate as then t needle |39 to the left as viewed in the drawings will cause the contact to disengage the contact |08 for a longer duration and the motor |22 will therefore rotate in a given direction. Upon deection of the galvanometer needle |39 to the right the motor will operate in the opposite direcftion due tothe disengagement of contact |99 from Contact ||2.

For the sake of simplicity and clarity in Fig. 5 I have omitted the usual permanent magnets associated with the galvanometer G. It will be evident to those skilled in the art however that the galvanometer G may be provided with such .magnets and other accessories as are usual, so

that the needle |39 will deiiect from the mid or neutral position in accordance with the energization of its Winding.

In Fig. 6 I illustrate a further modification of my invention wherein I employ a galvanometer contact mechanism as illustrated in Fig. 5, but maintain the electron discharge devices 26, lei normally non-conducting. It will be observed `that the contacts |08, m9 are connected byconductor MEA through resistance 62 to the terminal 68B of the secondary of the transformer te. When contacts iBS-i and ||l9| i2 are engaged during the half cycle when the anodes |27, |32 are positive with respect to the cathodcs H29, 34 the grids |28, |33 will be negative with respect "nected to ysaid thermocouple, means for adjustto the cathodes |29, ISB. Upon disengagement of contact |68 from contact the electron discharge device |26 will be rendered conducting, for the grid |28 will then be maintained at the potential of the cathode |29. Similarly, when contact I S disengagescontact ||2 the electron discharge |3| will be rendered conducting, as then the grid |33 will be maintained at the potential of the cathode |36. .It will be observed that the circuit arrangement illustrated in Fig. 6 and operation of motor |22 is substantially the same as that illustrated and described with reference to the embodiment of my invention shown in Figs. l and 2.l

` It will be understood that by describing and illustra-ting certain preferred embodiments of my invention I am not to be limited thereby except as to the appended claims in view ofthe prior art. What I claim as new, and desire to secure by Letters Patent of the United States, -is:

l. In a potentiometer pyrometer, in combination, a thermocouple producing an E. M. F. varying in non-linear relation to temperature, an.

adjustable slide wire resistance for balancing the potential generated by said thermocouple, a cam adjusted with said slide wire resistance having a shape corresponding to the non-linear relation between the thermocouple E. M. F. and temperal ture, and indicating means positioned by said cam whereby said indicating means is positioned in linear relation to the temperature producing said-thermocouple E. M. F.

ing said contact relative to said slide wire to maintain the vpotential drop through that portion of the slide Wire determined by the position of said con-tact equal to the E. M. F. produced by said thermocouple, a cam positioned by said lastnamedr means having a 'shape corresponding to the non-linear relation between thermocouple-E. M. F. and temperature, and exhibiting means positioned by said cam.

3. In a potentiometer pyrometer, inA combination, a thermocouple producing an E. M. F. varying withtemperature, a slide Wire resistance, a voltage source for producing a potential drop through said slide Wire, a contact engaging said slide wire connected to said thermocouple, means for adjusting'said contact relative to said slide wire to maintain the potential drop through that portion of the slide Wire determined by the position of said contact equal to the E. M F. produced by said thermocouple, a cam positioned by.

said last-named means having a shape corresponding to the relation between thermocouple E. M. F. and temperature, and exhibiting means positioned by said cam.

4. In a self-balancing potentiometer system, a motor havin-g a rotor operable in opposite directions, a circular disk mounted on said rotor having a slide wire resistance secured .to its periphery, a. cam mounted on said rotor, and exhibiting means positioned by said cam so that equal increments of motion of said exhibiting means correspond to unequal angular increments potentiometer, a circular chart having minimum and maximum graduations, an index movable relative to said' chart, a thermocouple producing I an E, M. F. varying with temperature, a cam for positioning said index relative to said chart, means responsive to said E. M. F. an-gularly positioning said' cam in correspondence with changes in said F.; said cam having a rise such that apredetermined selected change vin temperature will cause said index to be positioned from said minimum graduation to said maximum graduation.

7. In a self-balancing potentiometer p'yrometer, a scale having substantially uniform graduations, an index movable relative to said scale and exhibiting temperature, a cam for positioning said index relative to said scale, a thermocouple for producing an E. M. F. varying in non-linear relation to'temperature, means responsive to said E. M. F. for argularly positioning said cam in linear relation to changes in E. M. F.; said cam having a non-uniform rise so that said index is positioned in linear relation to changes in temperature.

8. In a circular chart' type of self-balancing potentiometer having -a thermo-couple with a non-linear output voltage characteristic, a balancing source of E, M. F.. a slide wire resistance and a contact movable relative thereto to balance the thermo-couple output and said E. M. F. and a reversible motor for relatively positioning said JOHN D. RYDER. 

